As a conventional power transmission device mounted on a vehicle and the like, for example, Patent Literature 1 discloses a power transmission device which is applied to a hybrid vehicle including both an internal combustion engine and an electric motor as power sources for travelling and has a first gear to which a drive force is input and a second gear which is meshed with the first gear in a state that it has a predetermined backlash and transmits the drive force to a load. When there is predicted an occurrence of collision between tooth surfaces due to a mesh between a first gear provided with a permanent magnet and a second gear provided with a coil disposed at a position where a magnetic flux from the permanent magnet links, the power transmission device reduces gear noise caused by a gear-tooth hammering shock without increasing a size of the device by controlling a current flowing to the coil by a control means so that the coil generates a flux linkage for suppressing a change of an interlinkage magnetic flux from the permanent magnet due to a change of an inter-tooth-surface relative distance.